As glasses having optical constants of a refractive index (nd) of 1.60 or more and less than 1.70 and an Abbe number (vd) of 50 or more and 56 or less, there are given SSK and LAK, the names of which are specified in Schott catalog. The glass transition point (Tg) of SSK and LAK is 600° C. or higher. In precision press molding, in which a lens is directly produced by press molding of softened glass, the molding temperature becomes 700° C. or higher. In the case where the temperature at the time of molding is high as described above, the reaction between the glass and the film of a molding die has become active, and sometimes, film detachment has occurred to degrade the productivity. Accordingly, in recent years, there have been developed glass having low Tg and glass having low yield point (At) each of which can lower the temperature at the time of being molded as glass for precision press molding.
Under the above circumstances, there are known various compositions as the glass for precision press molding, such as those described in U.S. Pat. Nos. 6,251,813, 7,015,164, and 4,226,627, and European Patent No. 0544494.